Manchester United have spent £7.4m to sign Tiago Manuel Dias Correia, otherwise known as Bébé, a relatively unknown 20-year-old from the Portuguese club Vitória de Guimarães, the Guardian can reveal. The deal was finalised today, with the player becoming the eighth senior striker at the club.

United have paid the buyout clause to release Bébé – was raised in an orphanage after spending part of his childhood on the streets and has represented Portugal in the Homeless World Cup – from his five-year contract at Guimarães only five weeks after he joined the club from Estrela da Amadora in the Portuguese third division.

He has been recommended to Sir Alex Ferguson by his former assistant, Carlos Queiroz, the Portugal national coach, and a deal has been rushed through for Bébé to become the third signing of the summer at Old Trafford. It takes the club's spending to around £25m following the arrival of Chris Smalling from Fulham and Javier Hernández from Chivas de Guadalajara, with Ferguson retaining a strong interest in Mesut Ozil, the Germany international.

The United manager was at Craven Cottage to see Ozil play in a pre-season friendly for Werder Bremen on Saturday and, although he tried to pass it off as watching a Premier League opponent, the Guardian has established he stayed back at the end of the match to talk to officials of the Bundesliga club in the boardroom. There remain a number of obstacles to clear, not least the fact that Chelsea, along with Real Madrid and, potentially, Barcelona are all interested.

The signing of Bébé has been far more straightforward, with Ferguson understood to have met the player for the first time yesterday when he flew to Portugal, principally to be a witness for Queiroz in a disciplinary case with the Portuguese football federation.

Bébé is described as a fast, technically gifted striker, right-footed and strong in the air and 6ft 2in tall. He has shown his potential with several goals in pre-season but his signing still represents a major surprise given Ferguson's recent insistence that he did not want to add to his squad and the player's low profile in Portuguese football.

Queiroz has convinced Ferguson that he may have unearthed a future gem and Bébé will provide competition for Wayne Rooney, Hernández, Dimitar Berbatov, Michael Owen and Federico Macheda, with Mame Biram Diouf having joined Blackburn Rovers on a season-long loan and Danny Welbeck on his way to Sunderland.